CT technology has been playing an important role in occasions such as safety inspection, thanks to its capability of eliminating influence from object overlapping, Conventional CT apparatuses use a slip ring device, and acquire projection data at different angles by rotating X-ray source and detectors. Then, the CT apparatuses reconstruct a tomogram image to obtain information of the inside of the inspected luggage or article. Multi-spectral analysis refers to identifying a material by using a difference in the material's absorption ability with respect to X-rays of different energy spectra. With a combination of the CT technology and the multi-spectral analysis, an existing inspection apparatus can reconstruct atomic number and electron density at any position within the inspected article, and identify a material contained in the article, achieving good effects in detecting substances like explosives or drugs.